HIV infection is known to be associated with progressive destruction of the immune system and particularly of T-lymphocytes expressing the CD4 phenotypic surface membrane markers, which are identified and enumerated in peripheral blood by flowcytometry. For any individual, the course of HIV infection has several possible outcomes: fast progression, slow progression and non-progression to CD4 depletion. Different rates of CD4 lymphocyte destruction and depletion are thought to explain these different outcomes, which may be mediated by differences in success of the immune response to viral infection as well as by other factors. The 4 specific aims of this protocol are as follows: 1) to develop QC-RT-PCR of CD4, CD8, Gag, Nef, and Vpu mRNA; 2) to define the correlation of CD4 and CD8 mRNA and their surface protein levels in both HIV negative and HIV positive individuals; 3) to develop molecular assays for immune functions, such as killing of HIV-infected cells by cytotoxic T-lymphocytes (CTL) which can be used to assess immune dysfunction in adult AIDS; 4) to define the progression of AIDS in the adult population using mRNAs that encode the CD4 and CD8 cell surface proteins, other important proteins of the immune system, and the above mentioned HIV proteins.